This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The DNA genetic information in our cells is packaged as chromatin. The nucleosome core particle is a fundamental repeating unit of chromatin and comprises about 150 base pairs of DNA spooled around a histone protein core. Recent studies show that chromatin is not simply a repressive structure that occludes DNA, but is instead an active participant in gene regulation that associates with multiple chromatin factors and enzymes. Despite the importance of such interactions, we currently lack a structural understanding of how chromatin factors or enzymes recognize the nucleosome. To address this problem, we have reconstituted complexes containing the nucleosome core particle and several chromatin factors or enzymes, and we have grown single crystals of a chromatin factor/nucleosome core particle complex. Our goal is to determine the three-dimensional structure of these chromatin factor/nucleosome complexes to understand how the cell recognizes and interacts with its genetic information assembled as chromatin.